A styroform packing material has been used for a long time for packing commodity and industrial products. Although the styroform package material has a merit such as a good thermal insulation performance, it has also various disadvantages: recycling the styroform is not possible, soot is produced when it burns, a flake or chip comes off when it is snagged because of it's brittleness, an expensive mold is needed for its production, and a relatively large warehouse is necessary to store it.
Therefore, to solve such problems above, other packing materials and methods have been proposed. One method is a fluid container of sealingly containing a liquid or gas. The fluid container has excellent characteristics to solve the problems in the styroform. First, because the container is made of only thin sheets, it does not need a large warehouse to store it unless the container is inflated. Secondly, a mold is not necessary for its production because of its simple structure. Thirdly, the fluid container does not produce a chip or dust which has adverse effect on precision products. Also, recyclable materials can be used for the films of the fluid container. Further, the fluid container can be produced with low cost.
FIG. 1A shows an example of fluid container in the conventional technology. The fluid container 10a is composed of first and second thermoplastic films 13 and 14, respectively, and a check valve 11. Typically, each thermoplastic film is composed of three layers of materials: polyethylene, nylon and polyethylene which are bonded together with appropriate adhesive. The first and second thermoplastic films are heat-sealed together around rectangular seal portions 12a, 12b after the check valve is attached. Thus, one container bag 10a sealed with the heat seal portions 12a, 12b is formed such as shown in FIG. 1A.
FIG. 1B shows an example of the manufacturing apparatus for the fluid container, including first and second plastic film stocks 13a and 14a respectively, a first heat seal device for attaching a check valve 11, a sensor device 16 to control for supplying elongated plastic films 13c and 14c, a second heat seal device 17 for right-left heat seal portions 12a, a third heat seal device 18 for upper-lower heat seal portions 12b, and film feed rollers 19.
Materials for the first and second plastic films are supplied as elongated plastic films 13b and 14b from the rolled film stocks 13a and 14a such as shown in FIG. 1B or FIG. 1C. The sensor device 16 is used to drive the feed rollers 19 and to control a feeding speed of the plastic films by, for example, by sensing marks printed on the elongated plastic film 13b or 14b. 
FIG. 1C shows an example of the first heat seal device 15, including upper and lower heat seal elements 15a and 15b, a check valve supplier 15c, heater assemblies 15d and check valves 11. The check valves 11 are pre-installed on the check valve supplier 15c. After the elongated films 13b, 14b for one container package are supplied, the check valve supplier 15c supplies the check valve 11 between the first and second elongated films 13b and 14b by rotating about its axis. The heater assemblies 15d are embedded in both the heat seal elements 15a-15b and maintain the surfaces to contact the films 13b and 14b at an appropriate fusing temperature of the plastic film. By sandwiching the check valve 11 between the upper and lower heat seal elements 15a and 15b, the check valve 11 is fused together with both the first and the second plastic films 13b, 14b and attached at a predetermined position of the fluid container.
Referring back to FIG. 1B, after installation of the check valve 11 at the stage of the first heat seal device 15, the elongated plastic films 13b, 14b are fused together to form the right-left heat seal portions 12a of the fluid container at the stage of the second heat seal device 17. Finally, the films 13b, 14b are fused together to form the upper-lower portions 12b at the stage of the third heat seal device 18, and the fluid container with one check valve shown in FIG. 1 is produced.
FIGS. 2A-2B show an example of a fluid container lob with multiple container members where each container member is provided with a check valve. A main purpose of having multiple container members is to increase the reliability. Namely, even if one of the container members causes an air leakage for some reason, the fluid container can still function as a cushion of package because other container members are intact. Thus, in order to achieve this purpose, each container member has an independent room which is inflated independently.
With reference to FIG. 2A, this fluid container 10b is made of the first and second thermoplastic films which are bonded together around a rectangular periphery 23a and further bonded together at each boundary of two container members 22 so that a guide passage 21 and container members 22 are created. When the first and second thermoplastic container films are bonded together, as shown in FIG. 2A, the check valves 11 are also attached to each inlet port of the container member 22. By attaching the check valves 11, each container member 22 becomes independent from the other. The inlet port 24 of the fluid container 10b is used when filling a fluid (typically an air) to each container member 22 by using, for example, an air compressor.
FIG. 2B shows an example of the fluid container 10b with multiple check valves when it is filled with the fluid. First, each container member 22 is filled with the fluid from the inlet port 24 through the guide passage 21 and the check valve 11. To avoid a rupture of the container members by variations in the environmental temperature, the fluid into the container is typically stopped when the container member 22 is inflated at about 90% of its full expansion rate. After filling the fluid, the expansion of each container member is maintained because each check-valve 11 prevents the reverse flow. Typically, the air compressor has a gage to monitor the supplied air pressure, and automatically stops supplying the air to the fluid container lob when the pressure reaches a predetermined value.
The check valve 11 is typically made of two rectangular thermoplastic valve films which are bonded together to form a fluid pipe. The fluid pipe has a tip opening and a valve body to allow a fluid flowing through the fluid pipe from the tip opening but to disallow the reverse flow through the valve body. More details of the check-valve example are described in the U.S. Pat. Nos. 5,209,264, 4,708,167 and 5,927,336. This type of check valve is produced before manufacturing the fluid container and attached to the fluid container as shown in FIG. 1C. Therefore, this type of check valve is often called an out-line valve. On the other hand, a valve which is produced in the process of making a fluid container, is called an in-line valve. Preferably, the present invention is applied to the in-line valve, although the present invention is also applicable to the out-line valve.
Fluid containers are becoming more and more popular. However, there are problems to solve, for example, when the fluid container 10b is inflated, both sides 23a and 23b of the check valve body is shifted inwardly by the expansion of the container member 22. The directions of the shift is shown by arrows 25 in FIG. 2C. As a result, the check valves 11 become wavy as shown in FIG. 2D although the bonded portion was straight before the fluid container 10b is inflated.
As mentioned above, the check valve 11 is typically made of two thermoplastic films. It should be noted that sometimes by the pressure noted above, a gap is created between the thermoplastic films 11a and the check-valve 11 of the container member 22. Thus, the fluid is leaked through the gap as shown in FIG. 2E. The leakage of the check valve 11a is shown by an arrow 27. In other words, the reverse flow in the container member corresponding to the check valve 11a occurs and the fluid from the container member 22 flows into the guide passage 21 in this example. This is a serious problem of the fluid containers in the conventional technology. As long as there is no gap between the two thermoplastic films, the reverse flow is prevented as shown in the wavy check valves 11b and 11c of FIG. 2E.
There is another problem which is involved in the production of the fluid containers. This problem is related to the installation of the check valves: it is not easy to accurately attach the check valve to each container member of the fluid container film. Therefore, the inaccurate installation of the check valve also sometimes causes a leakage problem.
As described in the foregoing, the fluid container using the check valves is highly useful for packing commodity products and industrial products instead of the styroform packing. However, since there are leakage and other problems in the fluid containers as described above, it is necessary to improve the performance of check valves in the fluid container and the production efficiency for producing the fluid containers to reduce the overall cost.